The present invention relates to an annular metal mold for vulcanizing and shaping an unvulcanized green tire. More particularly it relates to such annular metal mold which is composed of a combination of sector metal molds.
A tire vulcanizing metal mold has various protrusion patterns formed on its surface, and a groove pattern of a tire tread portion is formed by pressing a green tire onto this metal mold surface.
However, at the time of pressing a green tire onto a metal mold surface, air is apt to be confined between the metal mold surface and the green tire. Since a pattern is formed on a metal mold surface by protrusions, an escape path of air is blocked by these protrusions and a green tire, resulting in air traps, hence bares (recesses) are produced on a tire surface by these air traps. The commercial value of the tire is degraded.
Therefore, it has been a common practice to sever an annular metal mold into a plurality of smaller parts and to extract air by making use of gap clearances between adjacent smaller parts for preventing production of bares. In this case, each of the sector metal molds formed by severing an annular metal mold along the circumferential direction is composed of the above-mentioned smaller parts, and the annular metal mold is constructed by assembling these sector metal molds.
For instance in a tire vulcanizing metal mold disclosed in Laid-Open Japanese Utility Model Specification No. 2-17311 (1990), as shown in FIG. 11 three smaller parts 02 are assembled, and their backsides are supported by a reinforcement part 03 to construct one sector metal mold 01. These sector metal molds 01 are assembled in an annular form to form an annular metal mold. On the surface of the metal mold are formed protrusions 04, and a tread pattern of a tire is formed by this protrusion pattern.
In this tire vulcanizing metal mold, the smaller parts 02 have a shape formed by cutting and severing an annular metal mold along a circumferential direction by planes containing an axis of the tire, and joining surfaces of the sector metal mold 01 also form a plane.
The cutting surfaces between the smaller parts must be selectively provided at such portions that upon pressing a green tire, air may not be confined by the protrusion pattern. In addition, they must be provided by avoiding such places that cut portions of the protrusion may become thin-walled and liable to be broken and by avoiding blades or the like.
Accordingly, if a protrusion pattern becomes complicated, as shown in FIG. 12 (disclosed in Laid-Open Japanese Patent Specification No. 56-58817 (1981)), it becomes difficult to cut an annular metal mold 010 along a plane containing a tire axis, and hence it must be cut along an oblique plane L.sub.2 or a curved surface L.sub.3 without being limited to a plane L.sub.1 containing a tire axis.
In the example of the prior art disclosed in the above-referred Laid-Open Japanese Patent Specification No. 56-58817 (1981), smaller parts are made by cutting an annular metal mold 010 at desired cutting positions into a desired cut shape by means of a wire cutting tool.
In the case of assembling respective sector metal molds 01, an annular metal mold is constructed by making respective radially outwardly opened sector metal molds 01 slide towards their center. At this time, in order that the sector metal molds may be assembled with one another without any hindrance, joining surfaces 05 of the respective sector metal molds are formed into planes containing a tire axis as shown in FIG. 11.
It is also the same with respect to the case shown in FIG. 12, and even though smaller parts severed into arbitrary shapes are employed, for the smaller part forming a joining surface 05 of the sector metal mold, this particular joining surface 05 is formed into a plane containing a tire axis, but the other contour surfaces are formed into arbitrary shapes. Accordingly, this particular smaller part would be formed in a different shape from the other smaller parts not forming the joining surface 05 between the sector metal molds. As result, many kinds of smaller parts must be manufactured, hence working time is increased, and it becomes high in cost.
If the joining surfaces between the sector metal molds are formed in an arbitrary shape without any limitation, there is a fear that upon assembling a plurality of sector metal molds by making them slide towards the center, protrusion and recesses on the opposed joining surfaces 05 may not be well meshed with each other but may interfere with each other, resulting in damages.
Furthermore, when smaller parts are manufactured by cutting an annular metal mold into desired shapes as is the case of the above-referred Laid-Open Japanese Patent Specification No. 56-58817 (1981), special tools such as a wire cutting tool or the like are necessitated. Also it is necessary to control cutting by making use of a special program, and so, a lot of labor is necessitated for the cutting work.
The present invention has been worked out in view of the above-mentioned points, and one object of the present invention is to provide a metal mold for vulcanizing a tire, in which a plurality of smaller parts are made all in the same shape and construction time as well as a cost can be cut out, and a method for making the same metal mold.